In many communications systems, electronic signals are applied to a power amplifier before transmission. For example, in a base station of a cellular wireless communications system, electronic signals are applied to a power amplifier before being passed to an antenna for transmission over the air interface to the various subscribers.
Power amplifiers are designed such that they operate at maximum efficiency when their input signal levels are within a particular range.
In the case of a Wideband Code Division Multiple Access (WCDMA) or other Code Division Multiple Access (CDMA) system, data streams are multiplied with codes and added together. The composite signal is characterized by large variations in magnitude over time, which results in a large peak-to-average ratio (PAR). This reduces the efficiency of the power amplifiers to which these composite signals are applied before transmission, because the input signal levels are often outside the particular range within which the power amplifiers can operate with maximum efficiency. It is therefore highly desirable to reduce the PAR, without significantly degrading the transmitted signal.
The document “Effect of Clipping in Wideband CDMA System and Simple Algorithm for Peak Windowing”, O. Vaananen, J. Vankka and K. Halonen, World Wireless Congress, San Francisco, USA, May 28-31, 2002, pp. 614-619 describes a technique for reducing the PAR of a WCDMA signal. A windowing algorithm is applied to the signal, after upconversion to an intermediate frequency. More specifically, the document proposes the use of a windowing algorithm based on a Hamming function, which is a known mathematical function. The windowing algorithm is therefore known as a Hamming window.
However, the use of a Hamming window function requires the use of relatively large amounts of hardware to implement. This is a particular problem if a long window is used, although the use of a long window is advantageous from the point of view of improving the performance of the algorithm.
The possibility of an efficient implementation of the windowing function is particularly relevant when the device is to be implemented in a Field Programmable Gate Array (FPGA), when hardware resources are typically more limited than in a specifically designed integrated circuit, such as an ASIC.